A ballast provides power to a lamp and regulates the current and/or power provided to the lamp. Lamps, such as High Intensity Discharge (HID) lamps and fluorescent lamps require a ballast to provide the proper starting voltage for the lamp and to limit the operating current once the lamp is ignited. A ballast generally includes a power factor control (PFC) circuitry for sinusoidal input current control and generation of a regulated direct current (DC) bus voltage. Additionally, the ballast includes a lamp driver for providing a constant power to the lamp while the lamp is energized and compensating for fluctuations and fault conditions of the line voltage. While the lamp driver is providing current to the lamp, the lamp driver may also be configured to provide power for energizing the components of the ballast. The ballast may include a controller, such as a microcontroller for precisely controlling the PFC circuitry and the lamp driver. The controller may be further configured to perform features such as dimming, lamp fault detection, and end-of-life lamp monitoring.
The PFC circuitry, lamp driver, and controller must be energized before they can begin performing the functions discussed above. Conventional ballasts have used external power supply integrated chips in order to energize the components of the ballast while the ballast is starting up. However, such integrated chips add to the number of ballast components and increase the overall cost of the ballast. Currently known internal power supplies unnecessarily continue to dissipate power, after the ballast has finished starting up, while the lamp driver is providing power sufficient for energizing the ballast components.